Fixing arrangement

ABSTRACT

APPARATUS FOR FUSING ELECTROSCOPIC TONER IMAGES ONTO A SUPPORT IN WHICH A PAIR OF ELASTICALLY DEFORMABLE SHELL MEMBERS OF A GENERALLY CYLINDRICAL CONFIGURATION ARE EACH SUPPORTED IN A DEFORMED GENERALLY ELLIPTICAL CONFIGURATION ABOUT A PAIR OF GENERALLY PARALLEL SPACED ROLLER MEMBERS WITH THE ROLLER MEMBERS BEING BIASED IN A DIRECTION GENERALLY ALONG THE MINOR AXIS OF THE RESPECTIVE ELLIPTICAL CONFIGURATION TO FURTHER DEFORM AT LEAST A PROTION OF THE ELLIPTICAL SURFACE OF ONE OF THE SHELL MEMBERS AGAINST AT LEAST A PORTION OF THE ELLIPTICAL SURFACE OF THE OTHER OF THE SHELL MEMBERS THEREBY PROVIDING AN EXTENDED NIP OR AREA OF CONTACT BETWEEN THE SHELL MEMBERS. A SOURCE OF HEAT ENERGY ASSOCIATED WITH AT LEAST ONE OF THE SHELL MEMBERS PRODUCES A HEATING OF THE SHELL MEMBERS TO AN ELEVATED TEMPERATURE AND AS THE HEATED SHELL MEMBERS ARE ADVANCED ABOUT THE ROLLER MEMBERS IN THE DEFORMED CONFIGURATION A SUPPORT MEMBER HAVING UNFUSED ELECTROSCOPIC TONER IMAGES THEREON WILL BE ADVANCED THEREBETWEEN TO PRODUCE AT LEAST A PARTIAL MELTING OF THE TONER IMAGES ON THE SUPPORT WITHIN THE EXTENDED NIP AREA.

June 6, 1972 R C KAMQLA 3,667,742

FIXING ARRANGEMENT Filed Dec. 28, 1970 2 Sheets-Sheet 1 INVENTOR. ROMANC. KAMOLA ATTORNEY June 6, 1972 R. c. KAMOLA 3,567,742

FIXING ARRANGEMENT Filed Dec. 28, 1970 2 Sheets-Sheet 2 tates Patent US.Cl. 263-6 E 6 Claims ABSTRACT OF THE DISCLOSURE Apparatus for fusingelectroscopic toner images onto a support in which a pair of elasticallydeformable shell members of a generally cylindrical configuration areeach supported in a deformed generally elliptical configuration about apair of generally parallel spaced roller members with the roller membersbeing biased in a direction generally along the minor axis of therespective elliptical configuration to further deform at least a portionof the elliptical surface of one of the shell members against at least aportion of the elliptical surface of the other of the shell membersthereby providing an extended nip or area of contact between the shellmembers. A source of heat energy associated with at least one of theshell members produces a heating of the shell members to an elevatedtemperature and as the heated shell members are advanced about theroller members in the deformed configuration a support member havingunfuscd electroscopic toner images thereon will be advanced therebetweento produce at least a partial melting of the toner images on the supportwithin the extended nip area.

BACKGROUND OF THE INVENTION This invention relates generally to theaflixing of electroscopic toner material to a support member and moreparticularly to permanently affixing electroscopic toner material in animage configuration onto a support by the use of heat.

In order to permanently afiix or fuse an electroscopic toner materialonto a support member by heat, it is necessary to elevate thetemperature of the electroscopic toner material to a point at which atleast one of the constituents of the toner material is caused to melt.This action causes molten droplets of the toner material to form whichmolten droplets are absorbed to some extent in the fibers of the supportmember which in many instances constitutes paper so as to produce apermanent afiixation of the toner material on the support. Thereafter,as the toner material is cooled, solidification of the toner materialoccurs causing the toner material to be firmly bonded to the supportmaterial.

In both the electrographic recording art as well as the xerographic art,the use of heat for fixing toner images onto a support is old and wellknown. For example, one of the oldest and perhaps the most common heatfixing or fusing arrangements heretofore, has been the use of aresistance heating element which is supported in a refleeting deviceadjacent the support material. However, since in most such applications,the support material generally constitutes paper, such radiant heatingdevices have had an adverse affect on the support material itself. Thatis, in such fixing arrangements in order to insure sufficient fusion ofthe toner material to the paper, the temperature therein has been suchas to elevate the temperature of the paper as well as the toner beyond apoint so as to have deleterious effects on the paper. For example, inmost radiant fusing devices, not only is the temperature of the tonermaterial in image configuration elevated, the temperature of the papersupport also is elevated which 3,667,742 Patented June 6, 1972 "ice hasthe effect of evaporating and hence reducing the moisture contentnormally present within the paper material. This has the adverse affectof causing the paper to become brittle, as well as warping or inducing acurl therein. Accordingly, such radiant fusing arrangements haveheretofore been found generally unacceptable in many applications.

Another approach to fusing electroscopic toner images onto a support hasbeen passing the support with the toner images thereon between a pair ofopposed heated roller members. In this type of arrangement the tonerimages contact the heated surface of a roller member within the niptherebetween which produces a conductive heating of the toner imagewithin the nip.

In this type of arrangement however, because of the very small contactarea between roller member and image within the nip, a relatively highpressure contact between roller and image must be maintained if adequateheating of the image area is to be obtained. 'In addition, in sucharrangements, it is generally necessary to maintain the surface of theroller member at a fairly high temperature level to insure propermelting of the toner image within the relatively short time of contact.While this type of direct contact roller fuser has in many applicationsserved as a most effective fusing arrangement it nevertheless hascertain shortcomings largely due to the limited contact area providedbetween the roller members and the toner images, and the pressures andtemperatures required to produce adequate fusion of the toner images.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide improved apparatus for affixing electroscopic tonermaterial onto a support material.

It is a further object of the present invention to provide improvedapparatus for permanently affixing or fusing electroscopic tonermaterial onto a support member by the use of heat without adverselyalfecting the support material.

It is still another object of the present invention to provide animproved direct contact fusing apparatus.

It is still another object of the present invention to provide a directcontact fusing device having an extended contact nip.

It is still a further object of the present invention to provide adirect contact fusing device having a low initial warm up time.

It is yet a further object of the present invention to provide a highlyefiicient direct contact fusing device while preventing offset of thetoner images.

It is yet a further object of the present invention to provide a directcontact fusing device having an extended nip of contact which is adaptedfor simultaneous fusing of images on both sides of a support sheet.

These and other objects of the invention are attained by a firstelastically deformable shell member of a generally cylindricalconfiguration, a pair of roller members supported internally of saidfirst shell member in a generally parallel spaced relationship to eachother to elastically deform said shell member thereabout into agenerally elliptical configuration, a second elastically deformableshell member of a generally cylindrical configuration, a pair of rollermembers supported internally of said second shell member in a generallyparallel spaced relationship to each other to elastically deform saidsecond shell member thereabout into a generally ellipticalconfiguration, means operatively associated with said pairs of rollermembers for biasing said roller members in a direction generally alongthe minor axis of the respective elliptical configurations to furtherdeform at least a portion of the elliptical surface of one of the shellmembers against at least a portion of the eliptical surface of the otherof the shell members'to provide an extended nip between said shellmembers, heat generating means operatively associated with at least oneof said shell members for heating said shell member to an elevatedtemperature, and means operatively associated with said shell membersand said roller members for advancing said shell members about saidroller members in the deformed configuration to transport a supportmember having unfused electroscopic toner images thereon through theextended nip between said shell members to produce at least a partialmelting of said toner images on said support member.

' Other objects of the invention will become readily apparent to thoseskilled in the art in view of the following detailed disclosure anddescription thereof, especially when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration ofa system in which the fusing arrangement as contemplated by the presentinvention is particularly adapted for use.

FIG. 2 is an enlarged schematic illustration of the fusing arrangementillustrated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT According to the presentinvention electroscopic toner images which are to be permanently affixedto a support such as paper are contacted between a pair of members in anextended nip which are heated to a temperature sufficient to produce atleast a partial melting of the toner material. Within the area ofcontact, a transfer of the thermal energy in the heated members to thetoner material occurs. As at least a partial melting of the toner imageswithin the extended contact area is thus produced, the melted tonermaterial fiows to a certain extent into the fibers of the supportmaterial which after cooling readily adheres in a permanent manner tothe support material.

Although the invention will be described with particular reference totoner images which are formed through the now well-known xerographicprocess, it will be readily appreciated by those skilled in the art thatthe fusing arrangement as contemplated by the present invention is alsoreadily adaptable for permanently afiixing electroscopic toner imagesonto a support which have been produced by means of an electrographicrecording or electrostatic printing process.

Referring to FIG. 1, in which a xerographic reproducing apparatus hasbeen schematically illustrated, an original copy to be reproduced isplaced on a support tray 10 from-which it is fed into a feed apparatusgenerally a designated 11. On the feed apparatus the original is movedon an endless belt 12 driven by motor 13 to pass the optical axis ofprojection lens system 14 that is illuminated by a projection lampLMP-l. The image of the original is reflected by mirror 15 through anadjustable objective lens 16 and then reflected by mirror 17 downwardlythrough a variable slit aperture assembly 18 and onto the surface of axerographic plate in the form of a drum 19.

'Xerographic drum 19 includes a cylindrical member mounted in suitablebearings in the frame of the machine and is driven in a clockwisedirection by a motor 24 at a constant rate that is proportional to thetransport rate of the original, whereby the peripheral rate of the drumsurface is identical to the rate of movement of the projected radiationimage. The drum surface comprises a layer of photoconductive material ona conductive backing that is sensitized to exposure by means of a coronagenerating device 25 which may be an adaptation of the type disclosed inVyverberg Pat. No. 2,83 6,725 that is energized from a suitable highpotential source.

The exposure of the drum to the radiation image discharges thephotoconductive layer in the areas struck by radiation, whereby thereremains on the drum a latent electrostatic image in image configurationcorresponding to the radiation image projected from the original. As thedrum surface continues its movement, the electrostatic latent imagepasses through a developing station 26 at which a two-componentdeveloper material 27 which may be of the type disclosed in Walkup, Pat.No. 2,638,- 416, is cascaded over the drum surface by means ofdeveloping apparatus 28.

In the developing apparatus, developing material is carried up theconveyor 29, driven by suitable drive means from the motor 30, and thenreleased onto chute 31 whereby it is cascaded down over the drumsurface. The toner component 32 of the developer that is consumed indeveloping is stored in dispenser 33 and is dispensed in amountscontrolled by gate 34.

After developing, the xerographic powder image passes a dischargestation 41 at which the drum surface is illuminated by lamp LMP-2,whereby residual charges on the non-image areas of the drum surface arecompletely discharged. Thereafter, the powder image passes through animage transfer station 42 at which the power image is electrostaticallytransferred to a moving support surface 43 by means of a second coronagenerating device 44 similar to corona charging device 25', mentionedabove.

The moving support surface 43 to which the powder image is transferredmay be of any convenient type, such as paper, and may be obtained from asupply roll 45, fed over guide roll 46 and over tensioning roll 47,being directed into surface contact with the drum in the immediatevicinity of transfer corona generating device 44. After transfer, thesupport surface 43 is separated from the drum surface and guided throughthe fusing apparatus as contemplated by the present invention generallydesignated 48, wherein the powder image is permanently affixed thereto.Thereafter, the support surface may be fed over a further'system ofguide and tensioning rolls such as 49 and onto a take-up roll '52 thatis driven by motor 53.

After separation of the support surface 43 from the drum, a coronagenerating device 54 directs electrostatic charge to a residual powderimage on the drum surface. Thereafter, the xerographic drum surfacepasses through a cleaning station 55 at which the surface thereof isbrushed by a cleaning brush assembly 56, rotated by a motor 57, wherebyresidual developing material remaining on the drum surface is removed.The drum surface then passes through a second discharge station 58 atwhich it is illuminated by fluorescent lamp LMP-3, whereby the drumsurface in this region is completely flooded with light to remove anyelectrostatic charge that may remain thereon. Suitable light traps areprovided in the system to prevent any light rays from reaching the drumsurface, other than the projected image, during the period of drumtravel immediately prior to sensitization by corona generating device 25until after the drum surface has com pletely passed through thedeveloping station 26.

During operation of the xerographic apparatus, the image bearing supportsurface 43 carrying the loose powder images is moved through the fusingapparatus in a path accorded by the interrelation of rollers 47 and 49.While the support material 43 with the toner images 90 thereon has beenshown and described as being in the form of an elongated web it will beappreciated by those skilled in the art that the fusing arrangement ascontemplated by the present invention is equallyapplicable to the use ofsupport materials in the form of cut sheet stock.

The fusing apparatus 48 includes an insulating shell or jacket 60 whichsurrounds and encloses the active elements of the fusing assembly.Openings 73 and 74 at either side of insulating shell 60 in thedirection of support travel permit support member 43 with toner images90 thereon to pass through the fusing assembly with a minimal loss ofheat energy from the active elements of the fusing apparatus. Insulatingshell 60 may be composed of any suitable material which has a lowconductivity and emissivity of thermal energy.

The active elements of fusing apparatus 48 include shell members 61 and62 and roller members 63-64 and 65-66 respectively associated therewith.Shell members 61 and 62 are preferably formed from any suitableelastically deformable material which has a high conductivity andemissivity of thermal energy. Suitable materials include spring steels,stainless steels or alloys having high fatigue strength. Shell members61 and 62 in the normal undeformed condition are of a generallycylindrical configuration, the walls of which are thin in relation tothe size of the cylinder thus providing a low mass per unit surface areaof the shell members.

Roller members 63-64 and 6566 are likewise preferably formed from anysuitable material which has a high conductivity and emissivity ofthermal energy. Suitable materials include heat treated steels,stainless steels or alloys having high fatigue strength. Roller members63-64 and 65-66 like shell members 61 and 62 are of a generallycylindrical configuration and have wall thicknesses which are relativelythin in relation to the size of the respective cylinders. However,unlike shell members 61 and 62, roller members 63-64 and 6566 are,relatively speaking, rigidly non-deformable about their respectivecentral axes and maintain their general cylindrical configuration underan applied pressure. Shell members 61 and 62 on the other hand areelestically deformable about their respective axes while remainingnon-deformable through the dimensional thickness of the respectivewalls.

The roller members 63-64 and 6566 are supported internally of therespective shell members 61 and 62 in a generally parallel spacedrelationship to each other by any suitable support means which permitsrotational movement of the respective roller members about theirrespective central axes. By way of example, roller members 63-64 and6566 may be rotatably journaled at either end thereof in suitable frameplates operatively attached to either end of insulating jacket 60.

Roller members 63-64 and 6566 in their mounting arrangement are spacedfrom each other within the respective shell members 61 and 62 a distancesuflicient to elastically deform the respective shell members from thenormal cylindrical configurations against the normal elasticity of theshell material into generally elliptical configurations about therespective roller members. iRoller members 63-64 and 6566 in theirmounting arrangements are also biased or pressed in directions extendinggenerally along the minor axes of the respective ellipticalconfigurations to further deform at least a portion of the ellipticalsurface of one of the shell members against at least a portion of theelliptical surface of the other of the shell members to provide anextended nip or area of contact between the shell members 61 and 62 asmay be seen from FIG. 2 of the drawings.

Across the extended nip or area of contact between shell members 61 and62 a pressure will be exerted as a result of the deformation of theshell members 61 and 62 from the normal cylindrical configuration. Itwill be appreciated that by carefully balancing physical properties ofmaterials from which the shell members 61 and 62 are formed withappropriate wall thicknesses of the shell member, a wide latitude inpressures across the nip may be obtained. It will also be appreciatedthat with a proper choice of materials and relative dimensions,substantially uniform pressures may be obtained throughout the nip orextended area of contact.

To provide a heating of the toner images to be fused within the nip orextended area of contact, the active elements of the fusing apparatus 48are heated to an elevated temperature by suitable heat generating means.In the embodiment as illustrated in FIG. 2, a source of heat energy suchas quartz lamps 67 and 68 are located inwardly of shell members 61 and62 and extend as do shell members 61 and 72 in the lateral direction adistance sufiicient to encompass the width of support material 43 ontowhich images are to be fused. Lamps 67 and 68 are operatively connectedto a source of electrical energy and are adapted upon energization toproduce a heating of shell members 61 and 62 and roller members 63-64and 6566 to elevated temperatures sufficient to produce at least apartial melting of toner images on support member 43 which are passedthrough the nip or contact area between shell members 61 and 62.Suitable temperature responsive means such as heat sensor 72 may also beprovided to operatively control the enerization of quartz lamps 67 and68 and thereby maintain the temperature of the active elements of fusingapparatus 48 at a predetermined optimum level. In the embodiment of FIG.2 only one such sensing element 72 has been illustrated which issupported internally of roller member 64. However, it will beappreciated by those skilled in the art that additional sensing devicessuch as 72 may also be utilized to operatively control the energizationof quartz lamps 67 and 68 to thereby maintain the active elements offusing apparatus 48 within predetermined operating temperature ranges.

In the embodiment of fusing apparatus 48 as illustrated in FIG. 2, shellmembers 61 and 62 are preferably coated with a thin layer of materialsuch as polytetrafiuoroethylene. This coating of polytetrafiuoroethyleneor like material provides a fuser contact surface having a relativelyhigh repellancy for the toner particles as images are passed through thefusing apparatus 48. This polytetrafluoroethylene coating thereforeserves to prevent offsetting of the tacky or partially molten imagesonto shell members 61 and 62 as the images 90 pass through fusingapparatus 48. A light film of a suitable release agent may also beapplied to the surfaces of polytetrafluoroethylene coated shell members61 and 62 to further prevent against offsetting of the toner images 90onto the surfaces of shell members 61 and 62. To this end, a light filmof silicon oil for example, may be applied to the surfaces of shellmembers 61 and 62 by means of belts or ribbons 69 and 70 which areimpregnated with the release agent. In the embodiment of FIG. 2, beltsor ribbons 69 and 70 are disposed transversely to the direction ofmovement of shell members 61 and 62 and support member 43. As shellmembers 61 and 62 are driven about the roller members 63-64 and 6566 afilm of the release agent from belt members 69 and 70 Will be depositedon the surfaces of shell members 61 and 62. Suitable means may also beprovided for indexing belt members 69 and 70 over the surfaces of shellmembers 61 and 62 to maintain an adequate supply of the release agent toshell members 61 and 62.

In the embodiment of FIG. 2, shell members 61 and 62 are driven in theirdeformed configuration about roller members 63-64 and 6566 to transporta support member 43 having toner images 90 thereon through the fusingapparatus 48. In the embodiment of FIG. 2, roller member 65 is driven ina counterclockwise direction by means of a suitable drive arrangementexterior to the insulating shell 60. This may be accomplished by variouscombinations of gearing, belts, chain, etc. to drive roller member 65 ata predetermined rotational speed. In the embodiment as illustrated inFIG. 2, roller member 65 includes a plurality of sprocket teeth 71 whichare spaced about the periphery of the roller member 65 to impartmovement to shell members 61 and 72. In the preferred arrangement, afirst set of sprocket teeth 71 are located adjacent one end of rollermember 65 and a second set of sprocket teeth 71 are located adjacent theother end thereof. Sprocket teeth 71 on roller member 65 mesh withsuitably arranged apertures in roller member 63 to drive roller member63 in a clockwise direction as seen in FIG. 2. Sprocket teeth 71 onroller member 65 also mesh with suitably arranged apertures along theedges of shell members 61 and 72 to provide a positive driving force toshell members 61 and 62 in the directions as shown about idler rollers64 and 66 respectively. Thus as roller member 65 is driven from a sourceexternal to the fuser assembly 48, shell members 61 and 62 will *bedriven about roller members 63-64 and 65-66 respectively to transportsupport material 43 having unfused electroscopic toner images thereonthrough the fusing assembly. As will be appreciated however, otherequivalent drive arrangements may be employed for driving shell members61 and 62 about roller members 63-64 and 65-66 in the deformedconfiguration.

From the foregoing arrangement it will be appreciated that as shellmembers 61 and 62 of fusing apparatus 48 are driven in the directions asshown in FIG. 2, a support member 43 having images 90 thereon to befused will be transported through the extended nip or area of contactbetween shell members 61 and 62. -It should also be appreciated that asa result of the extended nip or area of contact that lies betweenopposite roller pairs 64-66 and 63-65, fusing of the toner images may beproduced at relatively lower contact pressures and at relatively lowertemperatures than has heretofore been possible in more conventionalcontact fusers. It should also be appreciated that as a result of therelatively low mass per unit area of shell members 61 and 62 and rollermembers 63-64 and 65-66 the fusing apparatus 48 requires a very shortinitial warm up time within which the active elements of the fusingapparatus reach optimum fusing temperature. It should also beappreciated that because of the relatively low mass per unit area of theactive elements of the fusing apparatus, the fusing apparatus thereforeis characterized by a quick thermal response time which enables anaccurate control between optimum fusing temperature limits. It should befurther appreciated that as a result of the substantially uniformpressure which is exerted within the extended area of contact, anoptimum heat transfer relationship is provided which continues over alonger period of time than has heretofore been possible withconventional 'contact fusers. Finally, it will be further appreciatedthat the fusing apparatus as contemplated by the present invention isideally adapted for fusing images which are not only placed on one sideof the support member but which are also placed on both sides of thesupport member, in a simultaneous manner.

While the invention has been described with reference to a preferredarrangement, it will be generally understood by those skilled in the artthat various changes may be made and equivalents may be substituted forelements thereof without departing from the true spirit and scope of theinvention.

What is claimed is:

1. Apparatus for fusing electroscopic toner images onto a supportcomprising,

a first elastically deformable shell member of a generally cylindricalconfiguration,

a pair of roller members supported internally of said first shell memberin a generally parallel spaced relationship to each other to elasticallydeform said shell member thereabout into a generally ellipticalconfiguration,

a second elastically deformable shell member of a generally cylindricalconfiguration,

a pair of roller members supported internally of said second shellmember in a generally parallel spaced relationship to each other toelastically deform said second shell member thereabout into a generallyelliptical configuration,

means operatively associated with said pairs of roller members forbiasing said roller members in a direction generally along the minoraxis of the respective elliptical configuration to further deform atleast a portion of the elliptical surface of one of the shell membersagainst at least a portion of the elliptical surface of the other of theshell members to provide an extended nip between said shell members,

'heat generating means operatively associated with at least one of saidshell members for heating said shell member to an elevated temperature,and

means operatively associated with said shell members and said rollermembers for advancing said shell members about said roller members inthe deformed configuration to transport a support member having unfusedelectroscopic toner images thereon through the extended nip between saidshell members to produce at least a partial melting of said toner imageson said support member.

2. Apparatus according to claim '1 further including,

applicator means for applying a quantity of offset preventing materialto the surface of said shell members.

3. Apparatus according to claim 1, said heat generating means including,

a first source of heat energy supported internally 0 said first shellmember adapted when energized to heat said first shell member to anelevated temperature,

a second source of heat energy supported internally of said second shellmember adapted when energized to heat said second shell member to anelevated temperature, and

means responsive to the temperature of said shell members forcontrolling the energization of said sources of heat energy.

4. Apparatus for affixing electroscopic toner images onto a supportcomprising,

a first generally cylindrically shaped thin shelled member formed from aheat conductive material of high elasticity,

a first pair of roller members supported for rotation about theirrespective axes internally of said thin shelled member, said rollermembers being spaced from each other in a generally parallelrelationship to elastically deform said thin shelled member thereaboutin a generally elliptical configuration,

a second generally cylindrically shaped thin shelled member formed froma heat conductive material of high elasticity,

a second pair of roller members supported for rotation about theirrespective axes internally of said thin shelled member, said rollermembers being spaced from each other in a generally parallelrelationship to elastically deform said thin shelled member thereaboutin a generally elliptical configuration,

fmeans operatively associated with said first and said second pairs ofroller members for biasing said roller members in. a direction generallyalong the minor axes of the elliptical configurations of said thinshelled members to further deform at least a portion of the ellipticalsurface of one of the thin shelled members against at least a portion ofthe elliptical surface of the other of the thin shelled members toprovide an extended nip between said first and said second thin shelledmembers,

heat generating means operatively associated with at least one of saidthin shelled members for heating said thin shelled member to an elevatedtemperature, and

means operatively associated with said thin shelled members and saidroller members for driving said thin shelled members about said rollermembers in the deformed configuration to advance a support member havingunfused electroscopic toner images on said support through the extendednip therebetween to produce at least a partial melting of said tonerimages on said support.

5. Apparatus to claim 4, said heat generating means including,

. a first source of heat energy supported internally of said first thinshelled member adapted when energized to heat said first thin shelledmember to an elevated temperature,

a second source of heat energy supported internally of said second thinshelled member adapted when energized to heat said second thin shelledmember to an elevated temperature, and

means responsive to the temperature of said thin shelled members forcontrolling the energization of said sources of heat energy.

6. Apparatus according to claim 5 further including,

applicator means for applying a quantity of ofiset 10 preventingmaterial to the surface of said thin shelled members.

References Cited UNITED STATES PATENTS 3,498,592 3/1970 Moser et a1.263-6E 3,539,161 11/ 1970 Byrne 2636 E 3,578,797 5/1971 Hodges 263--6 EX 0 3,584,195 6/1971 Vince 263-6 EX CHARLES J. MYHRE, Primary Examiner

